Sound volume controller for electronic musical instruments



NOV. 9, 1965 AKlRA NAKADA SOUND VOLUME CONTROLLER FOR ELECTRONIC MUSICAL INSTRUMENTS Filed Feb. 8, 1962 4 Sheets-Sheet 1 nib. C R. M wm m E E w m W nVDI TE mE GH S mm MM M R ma Mw A F HV HO AKH H C CV VIM VIM E U M M mm mm UR D EVA EM LE U UA U|| Elma m mM mM Wm WM WM a wm S S m y L F. F A w/ M L nl N ,w W f muy O .Dln S F. C S U ,Dn rr- A N E C R T C A L A ...IN v N ,s N U :NL L T|| A U U T Q C N k f 4.. D|n F .f C D ,f G Dn nw: m AD vI HOD U E O K Y E 4 m m 5550 .5950 A fwn y U Em t NG O T NOV. 9, 1965 AKIRA NAKADA SOUND VOIIUIIIIIEIv CONTROLLER FOR ELECTRONIC MUSICAL INSTRUMENTS Filed Feb. 8. 1962 4 Sheets-Sheet 2 r 1 I I l l I 1 I I I I l I I I I I I I I I All 1 Nov. 9, 1965 AKIRA NAKADA 3,217,081

SOUND VOLME CONTROLLER FOR ELECTRONIC MUSICAL INSTRUMENTS 4 Sheets-Sheet 3 Filed Feb. 8, 1962 Nov. 9, 1965 AKIRA NAKADA SOUND VOLUME CONTROLLER FOR ELECTRONIC MUSICAL INSTRUMENTS Filed Feb. 8, 1962 4 Sheets-Sheet 4 United States Patent O SOUND VOLUME CONTROLLER FOR ELEC- f TRONIC MUSICAL INSTRUMENTS Akira Nakada, Hermana-gun, Shizuoka-ken, Japan, as-

sgnor to Nippon Gakki Sezo Kabushiki Kaisha, Nakazawa-cho, Hamamtsu-shi, Japan, a joint-stock company of Japan Filed Feb. 8, 1962, Ser. No. 171,879 Claims. (Cl. 84-1.27)

This invention relates to means for controlling the volume, or intensity, of sound of electronic musical instruments, and more particularly it -relates to a new apparatus for controlling the sound volume of electronic musical instruments which apparatus utilizes inductance Variation as a variable element.

For a full land appreciative understanding of the nature and spirit of the present invention, the following points are presented for review. Music is a means of expressing human emotions by sound, and the methods of employing such means may be divided into two kinds, i.e., those using natural sounds and those using implements. Musical expression is greatly influenced by such elements as that relating to tempo, that relating to the degree of intensity of sound, and that relating -to loudness.

Electronic musical instruments, of course, belong to the kind of means of expression wherein implements are -used and are required to be such as to render various expressions by simple operations and simple skills. What is considered to be an extremely important element therein is the meansof controlling sound volume. An object of this invention is to provide a new and novel sound volume controller for electronic musical instruments, which is simple in construction and precise and easy in its volume controlling operation.

l The nature and details of the present invention will be clearly apparent by reference to the following description when taken in conjunction with the accompanying illustrations in which like parts are designated by like reference numerals or letters, and in which;

FIG. 1 is a block diagram indicating the larrangement of a representative electronic musical instrument to which the volume control means of the present invention is applied;

FIGURE 2 is a perspective view indicating a typical electronic musical instrument;

FIG. 3 is a schematic circuit diagram showing an electrical circuit suitable for lthe volume controller f shown in FIG. 2;

FIG. 4 is a graphical representation indicating the frequency characteristic of a volume controller a-ccording to the invention;

FIG. 5 is a perspective view indicating one embodiment of the present invention, utilizing a differential transformer which varies inductance;

FIG. 6 is a perspective view indicating another method of utilizing a differential transformer which varies inductance and representing an example of the case wherein a hollow core and a movable core adapted to slide in and slide out of said hollow core are used;

FIG. 7 is a side elevational View, in diagrammatic form, showing one example of a foot-Operated application of a volume controller of the invention to an electronic musical instrument;

. FIG. 8 is a perspective view, with parts cut away, showing the construction of a volume controller according to the invention;

FIG. 9a is a perspective view, with parts cut away, indicating a linkage for driving the moving core member of a transformer suitable for the embodiment of FIG. 8, in normal operation;

3,2 l 7,08 l Patented Nov. 9, 1965 ICC FIG. 9b is a perspective view of the linkage of FIG. 9a; and

FIGURE 9c is a perspective view of spring 21a.

A representative electronic musical instrument, as indicated in block form in FIG. l, comprises essentially -a tone source circuit A, a keying circuit B, a keyboard contact group C, a filter circuit D, a sound volume controller E, an accessory means F for accomplishing sound volume control, an amplifier G, and a loudspeaker system H.

The above essential parts are incorporated in such an electronic musical instrument as is representatively illustrated in FIG. 2. The controls of this instrument are: a swell keyboard a, a great keyboard b, a pedal keyboard c, stop levers d for tone control, a sustain lever e, and a sound volume controller f. The output music is emitted from a loundspeaker g.

The electrical circuit essential for the volume controller E of FIG. 1 comprises, as is shown in FIG. 3, a preamplifier section J, an impedance transducer section K for transducing the impedance of the signal power source, a volume control and low-pass filter section L, and a second preamplifier section M. In FIG. 3, the characters R1, R2, R13, 25, 27, 28, 29, and 30 and C1, 2, C5, C6, 23, 26 are, respectively, resistors and Condensers, and T1, T2, T3, T4 are transistors.

In one embodiment of this invention, the volume control and low-pass filter section L includes a tranformer which is composed of a primary coil 13, secondary coils 14 and 15, a ferromagnetic stationary core 16, and a moving magnetic material member 10. This transformer in practical construction has such adaptations as are illustrated in FIGS. 5, 6, and 8, as will be more fully described hereinafter.

The operation of the above-mentioned parts of an electronic musical instrument will now be described. The output electric oscillation of the electronic musical instrument is formed by the selection of tones by means of the key selection means B and C from the tone source A of the block diagram in FIG. 1 and the passage of these tones through the tone filter D. This output electric oscillation thus formed enters the first preamplifier J shown in FIG. 3 where it is amplified to a certain degree. In the case of this amplifier, the outer impedance is high, and the passing of this output, as it is, directly to a variable element is unsuitable for reasons of characteristics. Therefore, an impedance transducer section K becomes necessary. The signal electric oscillations passes through a capacitor 23 for suppressing direct current and -ows through the primary coil 13 of a differential transformer T. The said capacitor 23 has a low impedance with respect to alternating current.

The primary coil 13 and secondary coils 14 and 15 of the differential transformer T are disposed about a ferromagnetic stationary core 16 as shown in FIG. 5. When the electric oscillation current which has passed through the impedance transducer section K of FIG. 3 is caused to flow through the coil 13, magnetic iiux conforming to the electric oscillation is created in the magnetic core 16. If the resistance and the inductance of the two secondary coils 14 and 15 were identical, the potentials induced in both of the secondary coils 14 and 15 would also be equal in amplitude and phase. When the potentials induced in the two secondary coils 14 and 15 are combined in resistor 30 after passing through the identical resistors 28 and 29, the algebraic sum of the two potentials is obtained and is applied to the amplifier shown in the block M. If, however, the characteristics of one or the other of the two secondary coils 14 and 15 are modified so that the potentials induced in them are no longer identical but vary in `amplitude and phase,

then the algebraic sum of these potentials as applied to the input of the amplifier M may also be modified. It is feasible that the input potential to the amplifier M can be reduced to zero, if the potentials induced in the two secondary coils 14 and 15 are of equal amplitudes but opposite in phase. Thus, variation of the input signal to the amplifier M can range between zero and double the potential induced in either of the coils 14 and 15 One means for achievingv a variation`in the potentials induced in the coils 14 and 15 is by the construction shown in FIG. 5. The transformer shown in FIG. 5 comprises an E-shaped magnetic core 16 which supports the secondary coils 14 and 15 individually on each of its two outer legs and the primary winding 13 in its center leg. In addition, an I-member of magnetic material i's pivoted at one end on the end of the center leg of the core 16. The I-member 10 can be used to modify the magnetic paths between the primary winding 13 and the two secondary coils 14 and 15. When the I-member 10 is parallel to the center leg of the core 16, the two magnetic paths of the core 16 are the same, and the two secondary coils 14 and 15 will have identical potentials induced in them. When, however, the I-member 10 is moved from its central position parallel to the center leg of the core 16 toward either of the coils 14 and 15, then the reluctance of the magnetic path of one of the coils 14 or 15 will increase and that of the other will decrease. When the member 10 is moved into the position shown in FIG. 5 in heavy lines, then the reluctance of the magnetic path between the primary winding 13 and the secondary coil decreases below the path between the winding 13 and the coil 14. When the member 10 is in the position shown in faint lines in FIG. 5, then the reluctance of the magnetic path through the coil 15 is at a minimum and that of the path through the coil 14 is at a maximum. Thus, the relative coupling between the primary winding 13 and the two secondary coils 14 and 15 may be varied by changing the position of the member 10.

The sensitivity of the human ear varies greatly with frequency. That is, if the intensity of sound is reduced the tone of an electronic musical instrument will be heard as if it were also changed. In order to prevent this effect, it is necessary that the frequency characteristic at the time of balance (time of minimum sound volume) be such that the low-frequency tones and high-frequency tones must be raised as indicated inV FIG. 4. That is, it is necessary to carry out loudness control.

In the circuit of FIG. 3, the resistors 25 and 27 and the capacitor 26 constitute a low-pass lter, which governs the characteristic of the low-pass band of FIG. 4. The output from the impedance transducer K is taken across the resistance R12. The capacitor 26 is connected through the resistor 25 in parallel with resistor R12. Capacitor 26 varies in impedance with the frequency of the signal applied to it. Thus, it represents a lower impedance to a high frequency signal than it does to a low frequency signal. Therefore, `as the frequency of the signal across R12 rises, the effective parallel impedance of the R12 26 combination falls, and the effective potential of the higher frequency signals also falls. Since the impedance of the resistors 25 and 27 does not change with the frequency of the signals passing through them, the low pass filter 25, 27 and 26 passes the lower frequency signals very little changed and tends to short-circuit the higher frequency signals. The characteristic curves for high-frequency tones are governed by the ratio of the winding turns of the primary coil 13 and the secondary coils 14 and 15, as been confirmed experimentally. That is, it has been found that, in the high-frequency part, the above relation is due to the capacity caused by leakage between the windings.

When the relative impedances of the two secondary coils 14 and 15 are not quite the same due to manufacturing differences and differences in materials with the I-member 10 in its neutral position, a balance may be 4 achieved between the two by adjusting the potentiometer The load on the transformer T is purely resistive, and in' cludes the resistors 28, 29, and 30 as well as R13. The load, therefore, does not change with frequency. HOW- ever, as the position of the I-member 10 is varied, the mutual inductance, or coupling, between each of the two secondary coils 14 and 1S with the primary winding 13 is also varied. The closer the coupling, the more effective the load is upon the circuit. Therefore, as the I-member 10 is positioned close to the coil 15, the less elfect frequency has upon the coil 15 and the more it has upon the coil 14. However, as the member 10 is moved closer to coil 15, the inductance of the coil 14 increases, `and the lower the induced potential in it be-v comes. This modifies the signal potential applied by the transformer T to the amplier M. The filter tends to pass the lower frequency signals more strongly through the T-pad and the higher frequency signals more strongly through the transformed T. This occurs because the inductance of the coil 14 with the movements of the member 10, tends to decrease the amplitude of the high frequency signals. combined algebraically across the resistors 30 and 24, tending to cancel each other to some extent.

A variable resistor 24 is provided for the purpose of correcting any unbalance caused at time of winding. The state of balance can be determined by means of this resistor. Resistors 28 and 29 are provided for improvement of the frequency characteristics, and a resistor 30 is connected in series with the input impedance of the Preamplier M and functions as the load of the volume controller.

The afore-described modification of the balance between the induced voltages of the secondary coils 14 and 15 may be attained by the electro-mechanical mechanism as is shown in FIG. 5, wherein a moving core member 10 is rotatably supported on a pivotal shaft 18. A wedge-shaped core piece 11 -made of a magnetic substance is provided at the end of each leg of the ferromagnetic stationary core 16 so that, when the moving core member 10 approaches the ferromagnetic core 16, a sudden increase in the sound volume is prevented, and the afore-said balance is gradually changed.

On the basis of the foregoing principles, the volume controller may be reduced to a practical form of such a construction as is illustrated in FIG. 8. The embodiment shown in FIG. 8 comprises a volume controller body frame 2; a pedal plate 1 supported rotatably on a pivot shaft 4 supported in turn by the frame 2 and provided at its ends with retaining nuts 3; a differential transformer T which consists of a primary coil 13, secondary coils 14 and 15, a ferro-magnetic stationary core 16 of E type, and a moving core member 10, which is supported within the frame 2 by bracket 12ga linkage for transmitting movements of the pedal plate 1 to the afore-said moving core member `10, consisting of a bracket 7 fixed to the pedal plate 1, an L-shaped link 8 for a safety device, the link 8 and the bracket 7 being pivoted on a pin 20, and a driving link 9 pivoted to the link 8 by a pin 19 and to the afore-said moving core member 10 by a pin 17; and means such as members 5 and 6 for stopping the movement of the pedal plate 1 at the end of its operational stroke.

The pedal plate 1 is operated by a foot as indicated in FIG. 7 and can be depressed freely through an angle range of l0 to 45 degrees from horizontal until stopped by the afore-said means 5 and 6. By varying the angle of depression of this pedal plate 1, the sound volume is controlled during the playing of the musical instrument. The stop means 5 and 6 prevents the pedal plate Thus, the lower frequency signals are 1 from rotating through an angle greater than that necessary for volume control and is provided with material which will absorb surplus energy so as to prevent the emission of contact noise.

The mechanical system of the volume controller shown in FIG. 8 is provided with a safety device and a device for adjusting maximum value as illustrated in the enlarged perspective views of FIG. 9a and 9b. When the mechanical system is operating in a normal manner, the driving link 9, undergoes a movement indicated by the dotted :lines with the pin 19 as a center of rotation, as shown in FIG. 9a. If, however, an operational failure due to some cause occurs in the vicinity of the moving core member 10, and the system thereby is unable to move correctly, the safety device functions and rotates about the pin 20 as a center as indicated by the dotted lines in FIG. 9b, whereby a screw 22 separates away from the bracket 7. This is, although the moving core member 10 does not move, the force applied to the pedal plate 1 is absorbed by a spring 21a to prevent damake to the links 9 and 8 and pins 19 and 17.

Furthermore, a slight clearance between the moving core member 10 at the end of its full stroke at the time of maximum sound volume and the stationary core 16 is necessary in order to prevent collision between the two parts and emission of mechanical noise. This clearance is created and adjusted by the screw 22. When this screw 22 is turned, the link 8, rotating about the pin 20 as a center, varies its angular orientation relative to the bracket 7, andthe position of the pin 19 is shifted. As a result, the relative position of the pin 17 also changes. Thus, fine adjustment is possible. A spring 2lb is provided about the screw 22 to prevent loosening of the screw 22.

In the volume controller of the present invention, the differential inductance means need not be limited to a transformer such as that shown in FIG. 5 with ferromagnetic core, but may lbe a tube-type core transformer such as that indicated in FIG. 6. v

The transformer T of FIG. 5 can be modified so far as the inductance thereof can be continuously varied. For example, such a modified transformer is shown in FIG. 6, wherein a primary coil 13 is wound around a hollow ferromagnetic core 16 and secondary coils 14 and 15 are wound around said primary coil in spaced relation, and a movable core member 10 is disposed so as to slide in and slide out of said core 16. In this transformer, inductance of the circuit can be continuously varied in accordance with the position of the movable core relative to that of the stationary core 16.

Although this invention has been described with respect to a particular embodiment thereof, it is not to be so limited as changes and modifications may be made therein which are within the full intended scope of the invention, as defined by the appended claims.

What is claimed is:

1. In an electronic musical instrument having a frequency-amplitude characteristic which droops at the high and at the low frequencies at the higher amplitudes and which includes a tone source, means for compensating for said frequency-amplitude drooping characteristic, said compensating means comprising an amplifier for the output from said tone source, a variable filter circuit, means for connecting the output of said amplifier to the input of said filter circuit and for matching the output impedance of the amplifier with the input impedance of the filter circuit, said filter circuit comprising a resistancecapacitance T-pad low-pass circuit which tends to compensate for the drooping frequency-amplitude characteristic of said instrument at the low frequencies and a variable inductance device, said variable inductance device modifying the amplitude characteristics of said instrument, means for applying the signal output from said amplifier simultaneously to said low-pass circuit and to said inductance device, means for combining the output from the low-pass circuit and the output from said inductance device to provide an overall compensating characteristic which varies with amplitude, said inductance device comprising a pair of coils having a common input and being connected in parallel at one end and differentially at the other end, the output from said coils being taken from the paralleled end, and means for increasing the inductance of one of said coils with respect to the other of said coils so as to modify the signal output of said coils to be combined with the signal output from said low-pass circuit.

2. The instrument defined in claim 1 in which said inductance device comprises a transformer having a single primary winding as the common input and a pair of substantially identical secondary coils, a magnetic core passing through said primary winding and said pair of secondary coils, and means for differentially modifying the reluctance of the magnetic path coupling each of said secondary coils with said primary winding.

3. The instrument defined in claim 2 wherein said magnetic core comprises a generally E-shaped core having a secondary coil on each of its outer legs and the primary winding on the center leg, and further comprising an I-member pivoted on the end of the center leg and adjustable to decrease the air gap between the center leg and one of the outer legs.

4. The instrument defined in claim 3 wherein said inductance device is mounted in a housing, at least one portion of said housing being movable with respect to the rest of the housing, and means for connecting said I- member to said movable portion.

5. The instrument defined in claim 2 wherein said transformer comprises a hollow magnetic core having said secondary coils spaced apart thereon, and a magnetic slug movable through said hollow core to modify the coupling between said primary and one of said secondary coils.

References Cited by the Examiner UNITED STATES PATENTS 1,911,309 5/33 Coupleux et al.

2,085,927 7/37 Sorenson 325-415 X 2,142,580 1/ 39 Williams.

2,270,789 1/42 Smith 325-397 X 2,305,153 12/42 Fries 336-133 X 2,505,516 4/50 Bachman S25-399 X 2,563,899 8/51 Wiancko 336--133 X 2,569,521 10/51 Greaves et al.

2,698,360 12/54 Seybold 84-1.27 X 2,710,556 6/55 Koehl 84-1.27 X 2,911,873 11/59 Osborne 84-225 2,913,948 11/59 Bonham 84-1.19

ARTHUR GAUSS, Primary Examiner. ANTONIO F. GUIDA, Primary Examiner. 

1. IN AN ELECTRONIC MUSICAL INSTRUMENT HAVING A FREQUENCY-AMPLITUDE CHARACTERISTIC WHICH DROOPS AT THE HIGH AND AT THE LOW FREQUENCIES AT THE HIGHER AMPLITUDES AND WHICH INCLUDES A TONE SOURCE, MEANS FOR COMPENSATING FOR SAID FREQUENCY-AMPLITUDE DROOPING CHARACTERISTIC, SAID COMPENSATING MEANS COMPRISING AN AMPLIFITER FOR THE OUTPUT FROM SAID TONE SOURCE, A VARIABLE FILER CIRCUIT, MEANS FOR CONNECTING THE OUTPUT OF SAID AMPLIFIER TO THE INPUT OF SAID FILTER CIRCUIT AND FOR MATCHING THE OUTPUT IMPEDANCE OF THE AMPLIFIER WITH THE INPUT IMPEDANCE OF THE FILTER CIRCUIT, SAID FILTER CIRCUIT COMPRISING A RESISTANCECAPACITANCE T-PAD LOW-PASS CIRCUIT WHICH TENDS TO COMPENSATE FOR THE DROOPING FREQUENCY-AMPLITUDE CHARACTERISTIC OF SAID INSTRUMENT AT THE LOW FREQUENIES AND A VARIABLE INDUCTANCE DEVICE, SAID VARIABLE INDUCTANCE DEVICE MODIFYING THE AMPLITUDE CHARACTERISTICS OF SAID INSTRUMENT, MEANS FOR APPLYING THE SIGNAL OUTPUT FROM SAID AMPLIFIER SIMULTANEOUSLY TO SAID LOW-PASS CIRCUIT AND TO SAID INDUCTANCE DEVICE, MEANS FOR COMBINING THE OUTPUT FROM THE LOW-PASS CIRCUIT AND THE OUTPUT FROM SAID INDUCTANCE DEVICE TO PROVIDE AN OVERALL COMPENSATING CHARACTERISTIC WHICH VARIES WITH AMPLITUDE, SAID INDUCTANCE DEVICE COMPRISING A PAIR OF COILS HAVING A COMMON INPUT AND BEING CONNECTED IN PARALLEL AT ONE END AND DIFFERENTIALLY AT THE OTHER END, THE OUTPUT FROM SAID COILS BEING TAKEN FROM THE PARALLED END, AND MEANS FOR INCREASING THE INDUCTANCE OF ONE OF SAID COILS WITH RESPECT TO THE OTHER OF SAID COILS SO AS TO MODIFY THE SIGNAL OUTPUT OF SAID COILS TO BE COMBINED WITH THE SIGNAL OUTPUT FROM SAID LOW-PASS CIRCUIT. 